Multipoint touchscreen

ABSTRACT

A touch panel having a transparent capacitive sensing medium configured to detect multiple touches or near touches that occur at the same time and at distinct locations in the plane of the touch panel and to produce distinct signals representative of the location of the touches on the plane of the touch panel for each of the multiple touches is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/840,862, filed May 6, 2004 now U.S. Pat. No. 7,663,607, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an electronic device having atouch screen. More particularly, the present invention relates to atouch screen capable of sensing multiple points at the same time.

2. Description of the Related Art

There exist today many styles of input devices for performing operationsin a computer system. The operations generally correspond to moving acursor and/or making selections on a display screen. By way of example,the input devices may include buttons or keys, mice, trackballs, touchpads, joy sticks, touch screens and the like. Touch screens, inparticular, are becoming increasingly popular because of their ease andversatility of operation as well as to their declining price. Touchscreens allow a user to make selections and move a cursor by simplytouching the display screen via a finger or stylus. In general, thetouch screen recognizes the touch and position of the touch on thedisplay screen and the computer system interprets the touch andthereafter performs an action based on the touch event.

Touch screens typically include a touch panel, a controller and asoftware driver. The touch panel is a clear panel with a touch sensitivesurface. The touch panel is positioned in front of a display screen sothat the touch sensitive surface covers the viewable area of the displayscreen. The touch panel registers touch events and sends these signalsto the controller. The controller processes these signals and sends thedata to the computer system. The software driver translates the touchevents into computer events.

There are several types of touch screen technologies includingresistive, capacitive, infrared, surface acoustic wave, electromagnetic,near field imaging, etc. Each of these devices has advantages anddisadvantages that are taken into account when designing or configuringa touch screen. In resistive technologies, the touch panel is coatedwith a thin metallic electrically conductive and resistive layer. Whenthe panel is touched, the layers come into contact thereby closing aswitch that registers the position of the touch event. This informationis sent to the controller for further processing. In capacitivetechnologies, the touch panel is coated with a material that storeselectrical charge. When the panel is touched, a small amount of chargeis drawn to the point of contact. Circuits located at each corner of thepanel measure the charge and send the information to the controller forprocessing.

In surface acoustic wave technologies, ultrasonic waves are senthorizontally and vertically over the touch screen panel as for exampleby transducers. When the panel is touched, the acoustic energy of thewaves are absorbed. Sensors located across from the transducers detectthis change and send the information to the controller for processing.In infrared technologies, light beams are sent horizontally andvertically over the touch panel as for example by light emitting diodes.When the panel is touched, some of the light beams emanating from thelight emitting diodes are interrupted. Light detectors located acrossfrom the light emitting diodes detect this change and send thisinformation to the controller for processing.

One problem found in all of these technologies is that they are onlycapable of reporting a single point even when multiple objects areplaced on the sensing surface. That is, they lack the ability to trackmultiple points of contact simultaneously. In resistive and capacitivetechnologies, an average of all simultaneously occurring touch pointsare determined and a single point which falls somewhere between thetouch points is reported. In surface wave and infrared technologies, itis impossible to discern the exact position of multiple touch pointsthat fall on the same horizontal or vertical lines due to masking. Ineither case, faulty results are generated.

These problems are particularly problematic in tablet PCs where one handis used to hold the tablet and the other is used to generate touchevents. For example, as shown in FIGS. 1A and 1B, holding a tablet 2causes the thumb 3 to overlap the edge of the touch sensitive surface 4of the touch screen 5. As shown in FIG. 1A, if the touch technology usesaveraging, the technique used by resistive and capacitive panels, then asingle point that falls somewhere between the thumb 3 of the left handand the index finger 6 of the right hand would be reported. As shown inFIG. 1B, if the technology uses projection scanning, the technique usedby infra red and SAW panels, it is hard to discern the exact verticalposition of the index finger 6 due to the large vertical component ofthe thumb 3. The tablet 2 can only resolve the patches shown in gray. Inessence, the thumb 3 masks out the vertical position of the index finger6.

SUMMARY OF THE INVENTION

The invention relates, in one embodiment, to a touch panel having atransparent capacitive sensing medium configured to detect multipletouches or near touches that occur at the same time and at distinctlocations in the plane of the touch panel and to produce distinctsignals representative of the location of the touches on the plane ofthe touch panel for each of the multiple touches.

The invention relates, in another embodiment, to a display arrangement.The display arrangement includes a display having a screen fordisplaying a graphical user interface. The display arrangement furtherincludes a transparent touch panel allowing the screen to be viewedtherethrough and capable of recognizing multiple touch events that occurat different locations on the touch sensitive surface of the touchscreen at the same time and to output this information to a host device.

The invention relates, in another embodiment, to a computer implementedmethod. The method includes receiving multiple touches on the surface ofa transparent touch screen at the same time. The method also includesseparately recognizing each of the multiple touches. The method furtherincludes reporting touch data based on the recognized multiple touches.

The invention relates, in another embodiment, to a computer system. Thecomputer system includes a processor configured to execute instructionsand to carry out operations associated with the computer system. Thecomputer also includes a display device that is operatively coupled tothe processor. The computer system further includes a touch screen thatis operatively coupled to the processor. The touch screen is asubstantially transparent panel that is positioned in front of thedisplay. The touch screen is configured to track multiple objects, whichrest on, tap on or move across the touch screen at the same time. Thetouch screen includes a capacitive sensing device that is divided intoseveral independent and spatially distinct sensing points that arepositioned throughout the plane of the touch screen. Each sensing pointis capable of generating a signal at the same time. The touch screenalso includes a sensing circuit that acquires data from the sensingdevice and that supplies the acquired data to the processor.

The invention relates, in another embodiment, to a touch screen method.The method includes driving a plurality of sensing points. The methodalso includes reading the outputs from all the sensing lines connectedto the sensing points. The method further includes producing andanalyzing an image of the touch screen plane at one moment in time inorder to determine where objects are touching the touch screen. Themethod additionally includes comparing the current image to a past imagein order to determine a change at the objects touching the touch screen.

The invention relates, in another embodiment, to a digital signalprocessing method. The method includes receiving raw data. The raw dataincludes values for each transparent capacitive sensing node of a touchscreen. The method also includes filtering the raw data. The methodfurther includes generating gradient data. The method additionallyincludes calculating the boundaries for touch regions base on thegradient data. Moreover, the method includes calculating the coordinatesfor each touch region.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIGS. 1A and 1B show a user holding conventional touch screens.

FIG. 2 is a perspective view of a display arrangement, in accordancewith one embodiment of the present invention.

FIG. 3 shows an image of the touch screen plane at a particular point intime, in accordance with one embodiment of the present invention.

FIG. 4 is a multipoint touch method, in accordance with one embodimentof the present invention.

FIG. 5 is a block diagram of a computer system, in accordance with oneembodiment of the present invention.

FIG. 6 is a partial top view of a transparent multiple point touchscreen, in accordance with one embodiment of the present invention.

FIG. 7 is a partial top view of a transparent multi point touch screen,in accordance with one embodiment of the present invention.

FIG. 8 is a front elevation view, in cross section of a displayarrangement, in accordance with one embodiment of the present invention.

FIG. 9 is a top view of a transparent multipoint touch screen, inaccordance with another embodiment of the present invention.

FIG. 10 is a partial front elevation view, in cross section of a displayarrangement, in accordance with one embodiment of the present invention.

FIGS. 11A and 11B are partial top view diagrams of a driving layer and asensing layer, in accordance with one embodiment.

FIG. 12 is a simplified diagram of a mutual capacitance circuit, inaccordance with one embodiment of the present invention.

FIG. 13 is a diagram of a charge amplifier, in accordance with oneembodiment of the present invention.

FIG. 14 is a block diagram of a capacitive sensing circuit, inaccordance with one embodiment of the present invention.

FIG. 15 is a flow diagram, in accordance with one embodiment of thepresent invention.

FIG. 16 is a flow diagram of a digital signal processing method, inaccordance with one embodiment of the present invention.

FIGS. 17A-E show touch data at several steps, in accordance with oneembodiment of the present invention

FIG. 18 is a side elevation view of an electronic device, in accordancewith one embodiments of the present invention.

FIG. 19 is a side elevation view of an electronic device, in accordancewith one embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are discussed below with reference to FIGS.2-19. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these figures is forexplanatory purposes as the invention extends beyond these limitedembodiments.

FIG. 2 is a perspective view of a display arrangement 30, in accordancewith one embodiment of the present invention. The display arrangement 30includes a display 34 and a transparent touch screen 36 positioned infront of the display 34. The display 34 is configured to display agraphical user interface (GUI) including perhaps a pointer or cursor aswell as other information to the user. The transparent touch screen 36,on the other hand, is an input device that is sensitive to a user'stouch, allowing a user to interact with the graphical user interface onthe display 34. By way of example, the touch screen 36 may allow a userto move an input pointer or make selections on the graphical userinterface by simply pointing at the GUI on the display 34.

In general, touch screens 36 recognize a touch event on the surface 38of the touch screen 36 and thereafter output this information to a hostdevice. The host device may for example correspond to a computer such asa desktop, laptop, handheld or tablet computer. The host deviceinterprets the touch event and thereafter performs an action based onthe touch event. Conventionally, touch screens have only been capable ofrecognizing a single touch event even when the touch screen is touchedat multiple points at the same time (e.g., averaging, masking, etc.).Unlike conventional touch screens, however, the touch screen 36 shownherein is configured to recognize multiple touch events that occur atdifferent locations on the touch sensitive surface 38 of the touchscreen 36 at the same time. That is, the touch screen 36 allows formultiple contact points T1-T4 to be tracked simultaneously, i.e., iffour objects are touching the touch screen, then the touch screen tracksall four objects. As shown, the touch screen 36 generates separatetracking signals S1-S4 for each touch point T1-T4 that occurs on thesurface of the touch screen 36 at the same time. The number ofrecognizable touches may be about 15.15 touch points allows for all 10fingers, two palms and 3 others.

The multiple touch events can be used separately or together to performsingular or multiple actions in the host device. When used separately, afirst touch event may be used to perform a first action while a secondtouch event may be used to perform a second action that is differentthan the first action. The actions may for example include moving anobject such as a cursor or pointer, scrolling or panning, adjustingcontrol settings, opening a file or document, viewing a menu, making aselection, executing instructions, operating a peripheral deviceconnected to the host device etc. When used together, first and secondtouch events may be used for performing one particular action. Theparticular action may for example include logging onto a computer or acomputer network, permitting authorized individuals access to restrictedareas of the computer or computer network, loading a user profileassociated with a user's preferred arrangement of the computer desktop,permitting access to web content, launching a particular program,encrypting or decoding a message, and/or the like.

Recognizing multiple touch events is generally accomplished with amultipoint sensing arrangement. The multipoint sensing arrangement iscapable of simultaneously detecting and monitoring touches and themagnitude of those touches at distinct points across the touch sensitivesurface 38 of the touch screen 36. The multipoint sensing arrangementgenerally provides a plurality of transparent sensor coordinates ornodes 42 that work independent of one another and that representdifferent points on the touch screen 36. When plural objects are pressedagainst the touch screen 36, one or more sensor coordinates areactivated for each touch point as for example touch points T1-T4. Thesensor coordinates 42 associated with each touch point T1-T4 produce thetracking signals S1-S4.

In one embodiment, the touch screen 36 includes a plurality ofcapacitance sensing nodes 42. The capacitive sensing nodes may be widelyvaried. For example, the capacitive sensing nodes may be based on selfcapacitance or mutual capacitance. In self capacitance, the “self”capacitance of a single electrode is measured as for example relative toground. In mutual capacitance, the mutual capacitance between at leastfirst and second electrodes is measured. In either cases, each of thenodes 42 works independent of the other nodes 42 so as to producesimultaneously occurring signals representative of different points onthe touch screen 36.

In order to produce a transparent touch screen 36, the capacitancesensing nodes 42 are formed with a transparent conductive medium such asindium tin oxide (ITO). In self capacitance sensing arrangements, thetransparent conductive medium is patterned into spatially separatedelectrodes and traces. Each of the electrodes represents a differentcoordinate and the traces connect the electrodes to a capacitive sensingcircuit. The coordinates may be associated with Cartesian coordinatesystem (x and y), Polar coordinate system (r,θ) or some other coordinatesystem. In a Cartesian coordinate system, the electrodes may bepositioned in columns and rows so as to form a grid array with eachelectrode representing a different x, y coordinate. During operation,the capacitive sensing circuit monitors changes in capacitance thatoccur at each of the electrodes. The positions where changes occur andthe magnitude of those changes are used to help recognize the multipletouch events. A change in capacitance typically occurs at an electrodewhen a user places an object such as a finger in close proximity to theelectrode, i.e., the object steals charge thereby affecting thecapacitance.

In mutual capacitance, the transparent conductive medium is patternedinto a group of spatially separated lines formed on two differentlayers. Driving lines are formed on a first layer and sensing lines areformed on a second layer. Although separated by being on differentlayers, the sensing lines traverse, intersect or cut across the drivinglines thereby forming a capacitive coupling node. The manner in whichthe sensing lines cut across the driving lines generally depends on thecoordinate system used. For example, in a Cartesian coordinate system,the sensing lines are perpendicular to the driving lines thereby formingnodes with distinct x and y coordinates. Alternatively, in a polarcoordinate system, the sensing lines may be concentric circles and thedriving lines may be radially extending lines (or vice versa). Thedriving lines are connected to a voltage source and the sensing linesare connected to capacitive sensing circuit. During operation, a currentis driven through one driving line at a time, and because of capacitivecoupling, the current is carried through to the sensing lines at each ofthe nodes (e.g., intersection points). Furthermore, the sensing circuitmonitors changes in capacitance that occurs at each of the nodes. Thepositions where changes occur and the magnitude of those changes areused to help recognize the multiple touch events. A change incapacitance typically occurs at a capacitive coupling node when a userplaces an object such as a finger in close proximity to the capacitivecoupling node, i.e., the object steals charge thereby affecting thecapacitance.

By way of example, the signals generated at the nodes 42 of the touchscreen 36 may be used to produce an image of the touch screen plane at aparticular point in time. Referring to FIG. 3, each object in contactwith a touch sensitive surface 38 of the touch screen 36 produces acontact patch area 44. Each of the contact patch areas 44 covers severalnodes 42. The covered nodes 42 detect surface contact while theremaining nodes 42 do not detect surface contact. As a result, apixilated image of the touch screen plane can be formed. The signals foreach contact patch area 44 may be grouped together to form individualimages representative of the contact patch area 44. The image of eachcontact patch area 44 may include high and low points based on thepressure at each point. The shape of the image as well as the high andlow points within the image may be used to differentiate contact patchareas 44 that are in close proximity to one another. Furthermore, thecurrent image, and more particularly the image of each contact patcharea 44 can be compared to previous images to determine what action toperform in a host device.

Referring back to FIG. 2, the display arrangement 30 may be a standalone unit or it may integrated with other devices. When stand alone,the display arrangement 32 (or each of its components) acts like aperipheral device (monitor) that includes its own housing and that canbe coupled to a host device through wired or wireless connections. Whenintegrated, the display arrangement 30 shares a housing and is hardwired into the host device thereby forming a single unit. By way ofexample, the display arrangement 30 may be disposed inside a variety ofhost devices including but not limited to general purpose computers suchas a desktop, laptop or tablet computers, handhelds such as PDAs andmedia players such as music players, or peripheral devices such ascameras, printers and/or the like.

FIG. 4 is a multipoint touch method 45, in accordance with oneembodiment of the present invention. The method generally begins atblock 46 where multiple touches are received on the surface of the touchscreen at the same time. This may for example be accomplished by placingmultiple fingers on the surface of the touch screen. Following block 46,the process flow proceeds to block 47 where each of the multiple touchesis separately recognized by the touch screen. This may for example beaccomplished by multipoint capacitance sensors located within the touchscreen. Following block 47, the process flow proceeds to block 48 wherethe touch data based on multiple touches is reported. The touch data mayfor example be reported to a host device such as a general purposecomputer.

FIG. 5 is a block diagram of a computer system 50, in accordance withone embodiment of the present invention. The computer system 50 maycorrespond to personal computer systems such as desktops, laptops,tablets or handhelds. By way of example, the computer system maycorrespond to any Apple or PC based computer system. The computer systemmay also correspond to public computer systems such as informationkiosks, automated teller machines (ATM), point of sale machines (POS),industrial machines, gaming machines, arcade machines, vending machines,airline e-ticket terminals, restaurant reservation terminals, customerservice stations, library terminals, learning devices, and the like.

As shown, the computer system 50 includes a processor 56 configured toexecute instructions and to carry out operations associated with thecomputer system 50. For example, using instructions retrieved forexample from memory, the processor 56 may control the reception andmanipulation of input and output data between components of thecomputing system 50. The processor 56 can be a single-chip processor orcan be implemented with multiple components.

In most cases, the processor 56 together with an operating systemoperates to execute computer code and produce and use data. The computercode and data may reside within a program storage block 58 that isoperatively coupled to the processor 56. Program storage block 58generally provides a place to hold data that is being used by thecomputer system 50. By way of example, the program storage block mayinclude Read-Only Memory (ROM) 60, Random-Access Memory (RAM) 62, harddisk drive 64 and/or the like. The computer code and data could alsoreside on a removable storage medium and loaded or installed onto thecomputer system when needed. Removable storage mediums include, forexample, CD-ROM, PC-CARD, floppy disk, magnetic tape, and a networkcomponent.

The computer system 50 also includes an input/output (I/O) controller 66that is operatively coupled to the processor 56. The (I/O) controller 66may be integrated with the processor 56 or it may be a separatecomponent as shown. The I/O controller 66 is generally configured tocontrol interactions with one or more I/O devices. The I/O controller 66generally operates by exchanging data between the processor and the I/Odevices that desire to communicate with the processor. The I/O devicesand the I/O controller typically communicate through a data link 67. Thedata link 67 may be a one way link or two way link. In some cases, theI/O devices may be connected to the I/O controller 66 through wiredconnections. In other cases, the I/O devices may be connected to the I/Ocontroller 66 through wireless connections. By way of example, the datalink 67 may correspond to PS/2, USB, Firewire, IR, RF, Bluetooth or thelike.

The computer system 50 also includes a display device 68 that isoperatively coupled to the processor 56. The display device 68 may be aseparate component (peripheral device) or it may be integrated with theprocessor and program storage to form a desktop computer (all in onemachine), a laptop, handheld or tablet or the like. The display device68 is configured to display a graphical user interface (GUI) includingperhaps a pointer or cursor as well as other information to the user. Byway of example, the display device 68 may be a monochrome display, colorgraphics adapter (CGA) display, enhanced graphics adapter (EGA) display,variable-graphics-array (VGA) display, super VGA display, liquid crystaldisplay (e.g., active matrix, passive matrix and the like), cathode raytube (CRT), plasma displays and the like.

The computer system 50 also includes a touch screen 70 that isoperatively coupled to the processor 56. The touch screen 70 is atransparent panel that is positioned in front of the display device 68.The touch screen 70 may be integrated with the display device 68 or itmay be a separate component. The touch screen 70 is configured toreceive input from a user's touch and to send this information to theprocessor 56. In most cases, the touch screen 70 recognizes touches andthe position and magnitude of touches on its surface. The touch screen70 reports the touches to the processor 56 and the processor 56interprets the touches in accordance with its programming. For example,the processor 56 may initiate a task in accordance with a particulartouch.

In accordance with one embodiment, the touch screen 70 is capable oftracking multiple objects, which rest on, tap on, or move across thetouch sensitive surface of the touch screen at the same time. Themultiple objects may for example correspond to fingers and palms.Because the touch screen is capable of tracking multiple objects, a usermay perform several touch initiated tasks at the same time. For example,the user may select an onscreen button with one finger, while moving acursor with another finger. In addition, a user may move a scroll barwith one finger while selecting an item from a menu with another finger.Furthermore, a first object may be dragged with one finger while asecond object may be dragged with another finger. Moreover, gesturingmay be performed with more than one finger.

To elaborate, the touch screen 70 generally includes a sensing device 72configured to detect an object in close proximity thereto and/or thepressure exerted thereon. The sensing device 72 may be widely varied. Inone particular embodiment, the sensing device 72 is divided into severalindependent and spatially distinct sensing points, nodes or regions 74that are positioned throughout the touch screen 70. The sensing points74, which are typically hidden from view, are dispersed about the touchscreen 70 with each sensing point 74 representing a different positionon the surface of the touch screen 70 (or touch screen plane). Thesensing points 74 may be positioned in a grid or a pixel array whereeach pixilated sensing point 74 is capable of generating a signal at thesame time. In the simplest case, a signal is produced each time anobject is positioned over a sensing point 74. When an object is placedover multiple sensing points 74 or when the object is moved between orover multiple sensing point 74, multiple signals are generated.

The number and configuration of the sensing points 74 may be widelyvaried. The number of sensing points 74 generally depends on the desiredsensitivity as well as the desired transparency of the touch screen 70.More nodes or sensing points generally increases sensitivity, butreduces transparency (and vice versa). With regards to configuration,the sensing points 74 generally map the touch screen plane into acoordinate system such as a Cartesian coordinate system, a Polarcoordinate system or some other coordinate system. When a Cartesiancoordinate system is used (as shown), the sensing points 74 typicallycorrespond to x and y coordinates. When a Polar coordinate system isused, the sensing points typically correspond to radial (r) and angularcoordinates (θ).

The touch screen 70 may include a sensing circuit 76 that acquires thedata from the sensing device 72 and that supplies the acquired data tothe processor 56. Alternatively, the processor may include thisfunctionality. In one embodiment, the sensing circuit 76 is configuredto send raw data to the processor 56 so that the processor 56 processesthe raw data. For example, the processor 56 receives data from thesensing circuit 76 and then determines how the data is to be used withinthe computer system 50. The data may include the coordinates of eachsensing point 74 as well as the pressure exerted on each sensing point74. In another embodiment, the sensing circuit 76 is configured toprocess the raw data itself. That is, the sensing circuit 76 reads thepulses from the sensing points 74 and turns them into data that theprocessor 56 can understand. The sensing circuit 76 may performfiltering and/or conversion processes. Filtering processes are typicallyimplemented to reduce a busy data stream so that the processor 56 is notoverloaded with redundant or non-essential data. The conversionprocesses may be implemented to adjust the raw data before sending orreporting them to the processor 56. The conversions may includedetermining the center point for each touch region (e.g., centroid).

The sensing circuit 76 may include a storage element for storing a touchscreen program, which is a capable of controlling different aspects ofthe touch screen 70. For example, the touch screen program may containwhat type of value to output based on the sensing points 74 selected(e.g., coordinates). In fact, the sensing circuit in conjunction withthe touch screen program may follow a predetermined communicationprotocol. As is generally well known, communication protocols are a setof rules and procedures for exchanging data between two devices.Communication protocols typically transmit information in data blocks orpackets that contain the data to be transmitted, the data required todirect the packet to its destination, and the data that corrects errorsthat occur along the way. By way of example, the sensing circuit mayplace the data in a HID format (Human Interface Device).

The sensing circuit 76 generally includes one or more microcontrollers,each of which monitors one or more sensing points 74. Themicrocontrollers may for example correspond to an application specificintegrated circuit (ASIC), which works with firmware to monitor thesignals from the sensing device 72 and to process the monitored signalsand to report this information to the processor 56.

In accordance with one embodiment, the sensing device 72 is based oncapacitance. As should be appreciated, whenever two electricallyconductive members come close to one another without actually touching,their electric fields interact to form capacitance. In most cases, thefirst electrically conductive member is a sensing point 74 and thesecond electrically conductive member is an object 80 such as a finger.As the object 80 approaches the surface of the touch screen 70, a tinycapacitance forms between the object 80 and the sensing points 74 inclose proximity to the object 80. By detecting changes in capacitance ateach of the sensing points 74 and noting the position of the sensingpoints, the sensing circuit can recognize multiple objects, anddetermine the location, pressure, direction, speed and acceleration ofthe objects 80 as they are moved across the touch screen 70. Forexample, the sensing circuit can determine when and where each of thefingers and palm of one or more hands are touching as well as thepressure being exerted by the finger and palm of the hand(s) at the sametime.

The simplicity of capacitance allows for a great deal of flexibility indesign and construction of the sensing device 72. By way of example, thesensing device 72 may be based on self capacitance or mutualcapacitance. In self capacitance, each of the sensing points 74 isprovided by an individual charged electrode. As an object approaches thesurface of the touch screen 70, the object capacitive couples to thoseelectrodes in close proximity to the object thereby stealing charge awayfrom the electrodes. The amount of charge in each of the electrodes aremeasured by the sensing circuit 76 to determine the positions ofmultiple objects when they touch the touch screen 70. In mutualcapacitance, the sensing device 72 includes a two layer grid ofspatially separated lines or wires. In the simplest case, the upperlayer includes lines in rows while the lower layer includes lines incolumns (e.g., orthogonal). The sensing points 74 are provided at theintersections of the rows and columns. During operation, the rows arecharged and the charge capacitively couples to the columns at theintersection. As an object approaches the surface of the touch screen,the object capacitive couples to the rows at the intersections in closeproximity to the object thereby stealing charge away from the rows andtherefore the columns as well. The amount of charge in each of thecolumns is measured by the sensing circuit 76 to determine the positionsof multiple objects when they touch the touch screen 70.

FIG. 6 is a partial top view of a transparent multiple point touchscreen 100, in accordance with one embodiment of the present invention.By way of example, the touch screen 100 may generally correspond to thetouch screen shown in FIGS. 2 and 4. The multipoint touch screen 100 iscapable of sensing the position and the pressure of multiple objects atthe same time. This particular touch screen 100 is based on selfcapacitance and thus it includes a plurality of transparent capacitivesensing electrodes 102, which each represent different coordinates inthe plane of the touch screen 100. The electrodes 102 are configured toreceive capacitive input from one or more objects touching the touchscreen 100 in the vicinity of the electrodes 102. When an object isproximate an electrode 102, the object steals charge thereby affectingthe capacitance at the electrode 102. The electrodes 102 are connectedto a capacitive sensing circuit 104 through traces 106 that arepositioned in the gaps 108 found between the spaced apart electrodes102. The electrodes 102 are spaced apart in order to electricallyisolate them from each other as well as to provide a space forseparately routing the sense traces 106. The gap 108 is preferably madesmall so as to maximize the sensing area and to minimize opticaldifferences between the space and the transparent electrodes.

As shown, the sense traces 106 are routed from each electrode 102 to thesides of the touch screen 100 where they are connected to the capacitivesensing circuit 104. The capacitive sensing circuit 104 includes one ormore sensor ICs 110 that measure the capacitance at each electrode 102and that reports its findings or some form thereof to a host controller.The sensor ICs 110 may for example convert the analog capacitive signalsto digital data and thereafter transmit the digital data over a serialbus to a host controller. Any number of sensor ICs may be used. Forexample, a single chip may be used for all electrodes, or multiple chipsmay be used for a single or group of electrodes. In most cases, thesensor ICs 110 report tracking signals, which are a function of both theposition of the electrode 102 and the intensity of the capacitance atthe electrode 102.

The electrodes 102, traces 106 and sensing circuit 104 are generallydisposed on an optical transmissive member 112. In most cases, theoptically transmissive member 112 is formed from a clear material suchas glass or plastic. The electrode 102 and traces 106 may be placed onthe member 112 using any suitable patterning technique including forexample, deposition, etching, printing and the like. The electrodes 102and sense traces 106 can be made from any suitable transparentconductive material. By way of example, the electrodes 102 and traces106 may be formed from indium tin oxide (ITO). In addition, the sensorICs 110 of the sensing circuit 104 can be electrically coupled to thetraces 106 using any suitable techniques. In one implementation, thesensor ICs 110 are placed directly on the member 112 (flip chip). Inanother implementation, a flex circuit is bonded to the member 112, andthe sensor ICs 110 are attached to the flex circuit. In yet anotherimplementation, a flex circuit is bonded to the member 112, a PCB isbonded to the flex circuit and the sensor ICs 110 are attached to thePCB. The sensor ICs may for example be capacitance sensing ICs such asthose manufactured by Synaptics of San Jose, Calif., Fingerworks ofNewark, Del. or Alps of San Jose, Calif.

The distribution of the electrodes 102 may be widely varied. Forexample, the electrodes 102 may be positioned almost anywhere in theplane of the touch screen 100. The electrodes 102 may be positionedrandomly or in a particular pattern about the touch screen 100. Withregards to the later, the position of the electrodes 102 may depend onthe coordinate system used. For example, the electrodes 102 may beplaced in an array of rows and columns for Cartesian coordinates or anarray of concentric and radial segments for polar coordinates. Withineach array, the rows, columns, concentric or radial segments may bestacked uniformly relative to the others or they may be staggered oroffset relative to the others. Additionally, within each row or column,or within each concentric or radial segment, the electrodes 102 may bestaggered or offset relative to an adjacent electrode 102.

Furthermore, the electrodes 102 may be formed from almost any shapewhether simple (e.g., squares, circles, ovals, triangles, rectangles,polygons, and the like) or complex (e.g., random shapes). Further still,the shape of the electrodes 102 may have identical shapes or they mayhave different shapes. For example, one set of electrodes 102 may have afirst shape while a second set of electrodes 102 may have a second shapethat is different than the first shape. The shapes are generally chosento maximize the sensing area and to minimize optical differences betweenthe gaps and the transparent electrodes.

In addition, the size of the electrodes 102 may vary according to thespecific needs of each device. In some cases, the size of the electrodes102 corresponds to about the size of a finger tip. For example, the sizeof the electrodes 102 may be on the order of 4-5 mm2. In other cases,the size of the electrodes 102 are smaller than the size of the fingertip so as to improve resolution of the touch screen 100 (the finger caninfluence two or more electrodes at any one time thereby enablinginterpolation). Like the shapes, the size of the electrodes 102 may beidentical or they may be different. For example, one set of electrodes102 may be larger than another set of electrodes 102. Moreover, anynumber of electrodes 102 may be used. The number of electrodes 102 istypically determined by the size of the touch screen 100 as well as thesize of each electrode 102. In most cases, it would be desirable toincrease the number of electrodes 102 so as to provide higherresolution, i.e., more information can be used for such things asacceleration.

Although the sense traces 106 can be routed a variety of ways, they aretypically routed in manner that reduces the distance they have to travelbetween their electrode 102 and the sensor circuit 104, and that reducesthe size of the gaps 108 found between adjacent electrodes 102. Thewidth of the sense traces 106 are also widely varied. The widths aregenerally determined by the amount of charge being distributed therethrough, the number of adjacent traces 106, and the size of the gap 108through which they travel. It is generally desirable to maximize thewidths of adjacent traces 106 in order to maximize the coverage insidethe gaps 108 thereby creating a more uniform optical appearance.

In the illustrated embodiment, the electrodes 102 are positioned in apixilated array. As shown, the electrodes 102 are positioned in rows 116that extend to and from the sides of the touch screen 100. Within eachrow 116, the identical electrodes 102 are spaced apart and positionedlaterally relative to one another (e.g., juxtaposed). Furthermore, therows 116 are stacked on top of each other thereby forming the pixilatedarray. The sense traces 106 are routed in the gaps 108 formed betweenadjacent rows 106. The sense traces 106 for each row are routed in twodifferent directions. The sense traces 106 on one side of the row 116are routed to a sensor IC 110 located on the left side and the sensetraces 106 on the other side of the row 116 are routed to another sensorIC 110 located on the right side of the touch screen 100. This is doneto minimize the gap 108 formed between rows 116. The gap 108 may forexample be held to about 20 microns. As should be appreciated, thespaces between the traces can stack thereby creating a large gap betweenelectrodes. If routed to one side, the size of the space would besubstantially doubled thereby reducing the resolution of the touchscreen. Moreover, the shape of the electrode 102 is in the form of aparallelogram, and more particularly a parallelogram with sloping sides.

FIG. 7 is a partial top view of a transparent multi point touch screen120, in accordance with one embodiment of the present invention. In thisembodiment, the touch screen 120 is similar to the touch screen 100shown in FIG. 6, however, unlike the touch screen 100 of FIG. 6, thetouch screen 120 shown in FIG. 7 includes electrodes 122 with differentsizes. As shown, the electrodes 122 located in the center of the touchscreen 120 are larger than the electrodes 122 located at the sides ofthe touch screen 120. In fact, the height of the electrodes 122 getscorrespondingly smaller when moving from the center to the edge of thetouch screen 120. This is done to make room for the sense traces 124extending from the sides of the more centrally located electrodes 122.This arrangement advantageously reduces the gap found between adjacentrows 126 of electrodes 122. Although the height of each electrode 122shrinks, the height H of the row 126 as well as the width W of eachelectrode 122 stays the same. In one configuration, the height of therow 126 is substantially equal to the width of each electrode 122. Forexample, the height of the row 126 and the width of each electrode 122may be about 4 mm to about 5 mm.

FIG. 8 is a front elevation view, in cross section of a displayarrangement 130, in accordance with one embodiment of the presentinvention. The display arrangement 130 includes an LCD display 132 and atouch screen 134 positioned over the LCD display 132. The touch screenmay for example correspond to the touch screen shown in FIG. 6 or 7. TheLCD display 132 may correspond to any conventional LCD display known inthe art. Although not shown, the LCD display 132 typically includesvarious layers including a fluorescent panel, polarizing filters, alayer of liquid crystal cells, a color filter and the like.

The touch screen 134 includes a transparent electrode layer 136 that ispositioned over a glass member 138. The glass member 138 may be aportion of the LCD display 132 or it may be a portion of the touchscreen 134. In either case, the glass member 138 is a relatively thickpiece of clear glass that protects the display 132 from forces, whichare exerted on the touch screen 134. The thickness of the glass member138 may for example be about 2 mm. In most cases, the electrode layer136 is disposed on the glass member 138 using suitable transparentconductive materials and patterning techniques such as ITO and printing.Although not shown, in some cases, it may be necessary to coat theelectrode layer 136 with a material of similar refractive index toimprove the visual appearance of the touch screen. As should beappreciated, the gaps located between electrodes and traces do not havethe same optical index as the electrodes and traces, and therefore amaterial may be needed to provide a more similar optical index. By wayof example, index matching gels may be used.

The touch screen 134 also includes a protective cover sheet 140 disposedover the electrode layer 136. The electrode layer 136 is thereforesandwiched between the glass member 138 and the protective cover sheet140. The protective sheet 140 serves to protect the under layers andprovide a surface for allowing an object to slide thereon. Theprotective sheet 140 also provides an insulating layer between theobject and the electrode layer 136. The protective cover sheet 140 maybe formed from any suitable clear material such as glass and plastic.The protective cover sheet 140 is suitably thin to allow for sufficientelectrode coupling. By way of example, the thickness of the cover sheet140 may be between about 0.3-0.8 mm. In addition, the protective coversheet 140 may be treated with coatings to reduce sticktion when touchingand reduce glare when viewing the underlying LCD display 132. By way ofexample, a low sticktion/anti reflective coating 142 may be applied overthe cover sheet 140. Although the electrode layer 136 is typicallypatterned on the glass member 138, it should be noted that in some casesit may be alternatively or additionally patterned on the protectivecover sheet 140.

FIG. 9 is a top view of a transparent multipoint touch screen 150, inaccordance with another embodiment of the present invention. By way ofexample, the touch screen 150 may generally correspond to the touchscreen of FIGS. 2 and 4. Unlike the touch screen shown in FIGS. 6-8, thetouch screen of FIG. 9 utilizes the concept of mutual capacitance ratherthan self capacitance. As shown, the touch screen 150 includes a twolayer grid of spatially separated lines or wires 152. In most cases, thelines 152 on each layer are parallel one another. Furthermore, althoughin different planes, the lines 152 on the different layers areconfigured to intersect or cross in order to produce capacitive sensingnodes 154, which each represent different coordinates in the plane ofthe touch screen 150. The nodes 154 are configured to receive capacitiveinput from an object touching the touch screen 150 in the vicinity ofthe node 154. When an object is proximate the node 154, the objectsteals charge thereby affecting the capacitance at the node 154.

To elaborate, the lines 152 on different layers serve two differentfunctions. One set of lines 152A drives a current therethrough while thesecond set of lines 152B senses the capacitance coupling at each of thenodes 154. In most cases, the top layer provides the driving lines 152Awhile the bottom layer provides the sensing lines 152B. The drivinglines 152A are connected to a voltage source (not shown) that separatelydrives the current through each of the driving lines 152A. That is, thestimulus is only happening over one line while all the other lines aregrounded. They may be driven similarly to a raster scan. The sensinglines 152B are connected to a capacitive sensing circuit (not shown)that continuously senses all of the sensing lines 152B (always sensing).

When driven, the charge on the driving line 152A capacitively couples tothe intersecting sensing lines 152B through the nodes 154 and thecapacitive sensing circuit senses all of the sensing lines 152B inparallel. Thereafter, the next driving line 152A is driven, and thecharge on the next driving line 152A capacitively couples to theintersecting sensing lines 152B through the nodes 154 and the capacitivesensing circuit senses all of the sensing lines 152B in parallel. Thishappens sequential until all the lines 152A have been driven. Once allthe lines 152A have been driven, the sequence starts over (continuouslyrepeats). In most cases, the lines 152A are sequentially driven from oneside to the opposite side.

The capacitive sensing circuit typically includes one or more sensor ICsthat measure the capacitance in each of the sensing lines 152B and thatreports its findings to a host controller. The sensor ICs may forexample convert the analog capacitive signals to digital data andthereafter transmit the digital data over a serial bus to a hostcontroller. Any number of sensor ICs may be used. For example, a sensorIC may be used for all lines, or multiple sensor ICs may be used for asingle or group of lines. In most cases, the sensor ICs 110 reporttracking signals, which are a function of both the position of the node154 and the intensity of the capacitance at the node 154.

The lines 152 are generally disposed on one or more optical transmissivemembers 156 formed from a clear material such as glass or plastic. Byway of example, the lines 152 may be placed on opposing sides of thesame member 156 or they may be placed on different members 156. Thelines 152 may be placed on the member 156 using any suitable patterningtechnique including for example, deposition, etching, printing and thelike. Furthermore, the lines 152 can be made from any suitabletransparent conductive material. By way of example, the lines may beformed from indium tin oxide (ITO). The driving lines 152A are typicallycoupled to the voltage source through a flex circuit 158A, and thesensing lines 152B are typically coupled to the sensing circuit, andmore particularly the sensor ICs through a flex circuit 158B. The sensorICs may be attached to a printed circuit board (PCB). Alternatively, thesensor ICs may be placed directly on the member 156 thereby eliminatingthe flex circuit 158B.

The distribution of the lines 152 may be widely varied. For example, thelines 152 may be positioned almost anywhere in the plane of the touchscreen 150. The lines 152 may be positioned randomly or in a particularpattern about the touch screen 150. With regards to the later, theposition of the lines 152 may depend on the coordinate system used. Forexample, the lines 152 may be placed in rows and columns for Cartesiancoordinates or concentrically and radially for polar coordinates. Whenusing rows and columns, the rows and columns may be placed at variousangles relative to one another. For example, they may be vertical,horizontal or diagonal.

Furthermore, the lines 152 may be formed from almost any shape whetherrectilinear or curvilinear. The lines on each layer may be the same ordifferent. For example, the lines may alternate between rectilinear andcurvilinear. Further still, the shape of the opposing lines may haveidentical shapes or they may have different shapes. For example, thedriving lines may have a first shape while the sensing lines may have asecond shape that is different than the first shape. The geometry of thelines 152 (e.g., linewidths and spacing) may also be widely varied. Thegeometry of the lines within each layer may be identical or different,and further, the geometry of the lines for both layers may be identicalor different. By way of example, the linewidths of the sensing lines152B to driving lines 152A may have a ratio of about 2:1.

Moreover, any number of lines 152 may be used. It is generally believedthat the number of lines is dependent on the desired resolution of thetouch screen 150. The number of lines within each layer may be identicalor different. The number of lines is typically determined by the size ofthe touch screen as well as the desired pitch and linewidths of thelines 152.

In the illustrated embodiment, the driving lines 152A are positioned inrows and the sensing lines 152B are positioned in columns that areperpendicular to the rows. The rows extend horizontally to the sides ofthe touch screen 150 and the columns extend vertically to the top andbottom of the touch screen 150. Furthermore, the linewidths for the setof lines 152A and 152B are different and the pitch for set of lines 152Aand 152B are equal to one another. In most cases, the linewidths of thesensing lines 152B are larger than the linewidths of the driving lines152A. By way of example, the pitch of the driving and sensing lines 152may be about 5 mm, the linewidths of the driving lines 152A may be about1.05 mm and the linewidths of the sensing lines 152B may be about 2.10mm. Moreover, the number of lines 152 in each layer is different. Forexample, there may be about 38 driving lines and about 50 sensing lines.

As mentioned above, the lines in order to form semi-transparentconductors on glass, film or plastic, may be patterned with an ITOmaterial. This is generally accomplished by depositing an ITO layer overthe substrate surface, and then by etching away portions of the ITOlayer in order to form the lines. As should be appreciated, the areaswith ITO tend to have lower transparency than the areas without ITO.This is generally less desirable for the user as the user candistinguish the lines from the spaces therebetween, i.e., the patternedITO can become quite visible thereby producing a touch screen withundesirable optical properties. To further exacerbate this problem, theITO material is typically applied in a manner that produces a relativelylow resistance, and unfortunately low resistance ITO tends to be lesstransparent than high resistance ITO.

In order to prevent the aforementioned problem, the dead areas betweenthe ITO may be filled with indexing matching materials. In anotherembodiment, rather than simply etching away all of the ITO, the deadareas (the uncovered spaces) may be subdivided into unconnectedelectrically floating ITO pads, i.e., the dead areas may be patternedwith spatially separated pads. The pads are typically separated with aminimum trace width. Furthermore, the pads are typically made small toreduce their impact on the capacitive measurements. This techniqueattempts to minimize the appearance of the ITO by creating a uniformoptical retarder. That is, by seeking to create a uniform sheet of ITO,it is believed that the panel will function closer to a uniform opticalretarder and therefore non-uniformities in the visual appearance will beminimized. In yet another embodiment, a combination of index matchingmaterials and unconnected floating pads may be used.

FIG. 10 is a partial front elevation view, in cross section of a displayarrangement 170, in accordance with one embodiment of the presentinvention. The display arrangement 170 includes an LCD display 172 and atouch screen 174 positioned over the LCD display 170. The touch screenmay for example correspond to the touch screen shown in FIG. 9. The LCDdisplay 172 may correspond to any conventional LCD display known in theart. Although not shown, the LCD display 172 typically includes variouslayers including a fluorescent panel, polarizing filters, a layer ofliquid crystal cells, a color filter and the like.

The touch screen 174 includes a transparent sensing layer 176 that ispositioned over a first glass member 178. The sensing layer 176 includesa plurality of sensor lines 177 positioned in columns (extend in and outof the page). The first glass member 178 may be a portion of the LCDdisplay 172 or it may be a portion of the touch screen 174. For example,it may be the front glass of the LCD display 172 or it may be the bottomglass of the touch screen 174. The sensor layer 176 is typicallydisposed on the glass member 178 using suitable transparent conductivematerials and patterning techniques. In some cases, it may be necessaryto coat the sensor layer 176 with material of similar refractive indexto improve the visual appearance, i.e., make more uniform.

The touch screen 174 also includes a transparent driving layer 180 thatis positioned over a second glass member 182. The second glass member182 is positioned over the first glass member 178. The sensing layer 176is therefore sandwiched between the first and second glass members 178and 182. The second glass member 182 provides an insulating layerbetween the driving and sensing layers 176 and 180. The driving layer180 includes a plurality of driving lines 181 positioned in rows (extendto the right and left of the page). The driving lines 181 are configuredto intersect or cross the sensing lines 177 positioned in columns inorder to form a plurality of capacitive coupling nodes 182. Like thesensing layer 176, the driving layer 180 is disposed on the glass memberusing suitable materials and patterning techniques. Furthermore, in somecases, it may be necessary to coat the driving layer 180 with materialof similar refractive index to improve the visual appearance. Althoughthe sensing layer is typically patterned on the first glass member, itshould be noted that in some cases it may be alternatively oradditionally patterned on the second glass member.

The touch screen 174 also includes a protective cover sheet 190 disposedover the driving layer 180. The driving layer 180 is thereforesandwiched between the second glass member 182 and the protective coversheet 190. The protective cover sheet 190 serves to protect the underlayers and provide a surface for allowing an object to slide thereon.The protective cover sheet 190 also provides an insulating layer betweenthe object and the driving layer 180. The protective cover sheet issuitably thin to allow for sufficient coupling. The protective coversheet 190 may be formed from any suitable clear material such as glassand plastic. In addition, the protective cover sheet 190 may be treatedwith coatings to reduce sticktion when touching and reduce glare whenviewing the underlying LCD display 172. By way of example, a lowsticktion/anti reflective coating may be applied over the cover sheet190. Although the line layer is typically patterned on a glass member,it should be noted that in some cases it may be alternatively oradditionally patterned on the protective cover sheet.

The touch screen 174 also includes various bonding layers 192. Thebonding layers 192 bond the glass members 178 and 182 as well as theprotective cover sheet 190 together to form the laminated structure andto provide rigidity and stiffness to the laminated structure. Inessence, the bonding layers 192 help to produce a monolithic sheet thatis stronger than each of the individual layers taken alone. In mostcases, the first and second glass members 178 and 182 as well as thesecond glass member and the protective sheet 182 and 190 are laminatedtogether using a bonding agent such as glue. The compliant nature of theglue may be used to absorb geometric variations so as to form a singularcomposite structure with an overall geometry that is desirable. In somecases, the bonding agent includes an index matching material to improvethe visual appearance of the touch screen 170.

With regards to configuration, each of the various layers may be formedwith various sizes, shapes, and the like. For example, each of thelayers may have the same thickness or a different thickness than theother layers in the structure. In the illustrated embodiment, the firstglass member 178 has a thickness of about 1.1 mm, the second glassmember 182 has a thickness of about 0.4 mm and the protective sheet hasa thickness of about 0.55 mm. The thickness of the bonding layers 192typically varies in order to produce a laminated structure with adesired height. Furthermore, each of the layers may be formed withvarious materials. By way of example, each particular type of layer maybe formed from the same or different material. For example, any suitableglass or plastic material may be used for the glass members. In asimilar manner, any suitable bonding agent may be used for the bondinglayers 192.

FIGS. 11A and 11B are partial top view diagrams of a driving layer 200and a sensing layer 202, in accordance with one embodiment. In thisembodiment, each of the layers 200 and 202 includes dummy features 204disposed between the driving lines 206 and the sensing lines 208. Thedummy features 204 are configured to optically improve the visualappearance of the touch screen by more closely matching the opticalindex of the lines. While index matching materials may improve thevisual appearance, it has been found that there still may exist somenon-uniformities. The dummy features 204 provide the touch screen with amore uniform appearance. The dummy features 204 are electricallyisolated and positioned in the gaps between each of the lines 206 and208. Although they may be patterned separately, the dummy features 204are typically patterned along with the lines 206 and 208. Furthermore,although they may be formed from different materials, the dummy features204 are typically formed with the same transparent conductive materialas the lines as for example ITO to provide the best possible indexmatching. As should be appreciated, the dummy features will more thanlikely still produce some gaps, but these gaps are much smaller than thegaps found between the lines (many orders of magnitude smaller). Thesegaps, therefore have minimal impact on the visual appearance. While thismay be the case, index matching materials may be additionally applied tothe gaps between the dummy features to further improve the visualappearance of the touch screen. The distribution, size, number,dimension, and shape of the dummy features may be widely varied.

FIG. 12 is a simplified diagram of a mutual capacitance circuit 220, inaccordance with one embodiment of the present invention. The mutualcapacitance circuit 220 includes a driving line 222 and a sensing line224 that are spatially separated thereby forming a capacitive couplingnode 226. The driving line 222 is electrically coupled to a voltagesource 228, and the sensing line 224 is electrically coupled to acapacitive sensing circuit 230. The driving line 222 is configured tocarry a current to the capacitive coupling node 226, and the sensingline 224 is configured to carry a current to the capacitive sensingcircuit 230. When no object is present, the capacitive coupling at thenode 226 stays fairly constant. When an object 232 such as a finger isplaced proximate the node 226, the capacitive coupling changes throughthe node 226 changes. The object 232 effectively shunts some of thefield away so that the charge projected across the node 226 is less. Thechange in capacitive coupling changes the current that is carried by thesensing lines 224. The capacitive sensing circuit 230 notes the currentchange and the position of the node 226 where the current changeoccurred and reports this information in a raw or in some processed formto a host controller. The capacitive sensing circuit does this for eachnode 226 at about the same time (as viewed by a user) so as to providemultipoint sensing.

The sensing line 224 may contain a filter 236 for eliminating parasiticcapacitance 237, which may for example be created by the large surfacearea of the row and column lines relative to the other lines and thesystem enclosure at ground potential. Generally speaking, the filterrejects stray capacitance effects so that a clean representation of thecharge transferred across the node 226 is outputted (and not anything inaddition to that). That is, the filter 236 produces an output that isnot dependent on the parasitic capacitance, but rather on thecapacitance at the node 226. As a result, a more accurate output isproduced.

FIG. 13 is a diagram of an inverting amplifier 240, in accordance withone embodiment of the present invention. The inverting amplifier 240 maygenerally correspond to the filter 236 shown in FIG. 12. As shown, theinverting amplifier includes a non inverting input that is held at aconstant voltage (in this case ground), an inverting input that iscoupled to the node and an output that is coupled to the capacitivesensing circuit 230. The output is coupled back to the inverting inputthrough a capacitor. During operation, the input from the node may bedisturbed by stray capacitance effects, i.e., parasitic capacitance. Ifso, the inverting amplifier is configured to drive the input back to thesame voltage that it had been previously before the stimulus. As such,the value of the parasitic capacitance doesn't matter.

FIG. 14 is a block diagram of a capacitive sensing circuit 260, inaccordance with one embodiment of the present invention. The capacitivesensing circuit 260 may for example correspond to the capacitive sensingcircuits described in the previous figures. The capacitive sensingcircuit 260 is configured to receive input data from a plurality ofsensing points 262 (electrode, nodes, etc.), to process the data and tooutput processed data to a host controller.

The sensing circuit 260 includes a multiplexer 264 (MUX). Themultiplexer 264 is a switch configured to perform time multiplexing. Asshown, the MUX 264 includes a plurality of independent input channels266 for receiving signals from each of the sensing points 262 at thesame time. The MUX 264 stores all of the incoming signals at the sametime, but sequentially releases them one at a time through an outputchannel 268.

The sensing circuit 260 also includes an analog to digital converter 270(ADC) operatively coupled to the MUX 264 through the output channel 268.The ADC 270 is configured to digitize the incoming analog signalssequentially one at a time. That is, the ADC 270 converts each of theincoming analog signals into outgoing digital signals. The input to theADC 270 generally corresponds to a voltage having a theoreticallyinfinite number of values. The voltage varies according to the amount ofcapacitive coupling at each of the sensing points 262. The output to theADC 270, on the other hand, has a defined number of states. The statesgenerally have predictable exact voltages or currents.

The sensing circuit 260 also includes a digital signal processor 272(DSP) operatively coupled to the ADC 270 through another channel 274.The DSP 272 is a programmable computer processing unit that works toclarify or standardize the digital signals via high speed mathematicalprocessing. The DSP 274 is capable of differentiating between human madesignals, which have order, and noise, which is inherently chaotic. Inmost cases, the DSP performs filtering and conversion algorithms usingthe raw data. By way of example, the DSP may filter noise events fromthe raw data, calculate the touch boundaries for each touch that occurson the touch screen at the same time, and thereafter determine thecoordinates for each touch event. The coordinates of the touch eventsmay then be reported to a host controller where they can be compared toprevious coordinates of the touch events to determine what action toperform in the host device.

FIG. 15 is a flow diagram 280, in accordance with one embodiment of thepresent invention. The method generally begins at block 282 where aplurality of sensing points are driven. For example, a voltage isapplied to the electrodes in self capacitance touch screens or throughdriving lines in mutual capacitance touch screens. In the later, eachdriving line is driven separately. That is, the driving lines are drivenone at a time thereby building up charge on all the intersecting sensinglines. Following block 282, the process flow proceeds to block 284 wherethe outputs (voltage) from all the sensing points are read. This blockmay include multiplexing and digitizing the outputs. For example, inmutual capacitance touch screens, all the sensing points on one row aremultiplexed and digitized and this is repeated until all the rows havebeen sampled. Following block 284, the process flow proceeds to block286 where an image or other form of data (signal or signals) of thetouch screen plane at one moment in time can be produced and thereafteranalyzed to determine where the objects are touching the touch screen.By way of example, the boundaries for each unique touch can becalculated, and thereafter the coordinates thereof can be found.Following block 286, the process flow proceeds to block 288 where thecurrent image or signal is compared to a past image or signal in orderto determine a change in pressure, location, direction, speed andacceleration for each object on the plane of the touch screen. Thisinformation can be subsequently used to perform an action as for examplemoving a pointer or cursor or making a selection as indicated in block290.

FIG. 16 is a flow diagram of a digital signal processing method 300, inaccordance with one embodiment of the present invention. By way ofexample, the method may generally correspond to block 286 shown anddescribed in FIG. 15. The method 300 generally begins at block 302 wherethe raw data is received. The raw data is typically in a digitized form,and includes values for each node of the touch screen. The values may bebetween 0 and 256 where 0 equates to the highest capacitive coupling (notouch pressure) and 256 equates to the least capacitive coupling (fulltouch pressure). An example of raw data at one point in time is shown inFIG. 17A. As shown in FIG. 17A, the values for each point are providedin gray scale where points with the least capacitive coupling are shownin white and the points with the highest capacitive coupling are shownin black and the points found between the least and the highestcapacitive coupling are shown in gray.

Following block 302, the process flow proceeds to block 304 where theraw data is filtered. As should be appreciated, the raw data typicallyincludes some noise. The filtering process is configured to reduce thenoise. By way of example, a noise algorithm may be run that removespoints that aren't connected to other points. Single or unconnectedpoints generally indicate noise while multiple connected pointsgenerally indicate one or more touch regions, which are regions of thetouch screen that are touched by objects. An example of a filtered datais shown in FIG. 17B. As shown, the single scattered points have beenremoved thereby leaving several concentrated areas.

Following block 304, the process flow proceeds to block 306 wheregradient data is generated. The gradient data indicates the topology ofeach group of connected points. The topology is typically based on thecapacitive values for each point. Points with the lowest values aresteep while points with the highest values are shallow. As should beappreciated, steep points indicate touch points that occurred withgreater pressure while shallow points indicate touch points thatoccurred with lower pressure. An example of gradient data is shown inFIG. 17C.

Following block 306, the process flow proceeds to block 308 where theboundaries for touch regions are calculated based on the gradient data.In general, a determination is made as to which points are groupedtogether to form each touch region. An example of the touch regions isshown in FIG. 17D.

In one embodiment, the boundaries are determined using a watershedalgorithm. Generally speaking, the algorithm performs imagesegmentation, which is the partitioning of an image into distinctregions as for example the touch regions of multiple objects in contactwith the touchscreen. The concept of watershed initially comes from thearea of geography and more particularly topography where a drop of waterfalling on a relief follows a descending path and eventually reaches aminimum, and where the watersheds are the divide lines of the domains ofattracting drops of water. Herein, the watershed lines represent thelocation of pixels, which best separate different objects touching thetouch screen. Watershed algorithms can be widely varied. In oneparticular implementation, the watershed algorithm includes formingpaths from low points to a peak (based on the magnitude of each point),classifying the peak as an ID label for a particular touch region,associating each point (pixel) on the path with the peak. These stepsare performed over the entire image map thus carving out the touchregions associated with each object in contact with the touchscreen.

Following block 308, the process flow proceeds to block 310 where thecoordinates for each of the touch regions are calculated. This may beaccomplished by performing a centroid calculation with the raw dataassociated with each touch region. For example, once the touch regionsare determined, the raw data associated therewith may be used tocalculate the centroid of the touch region. The centroid may indicatethe central coordinate of the touch region. By way of example, the X andY centroids may be found using the following equations:Xc=ΣZ*x/ΣZ; andYc=ΣZ*y/ΣZ,

where

Xc represents the x centroid of the touch region

Yc represents the y centroid of the touch region

x represents the x coordinate of each pixel or point in the touch region

y represents the y coordinate of each pixel or point in the touch region

Z represents the magnitude (capacitance value) at each pixel or point

An example of a centroid calculation for the touch regions is shown inFIG. 17E. As shown, each touch region represents a distinct x and ycoordinate. These coordinates may be used to perform multipoint trackingas indicated in block 312. For example, the coordinates for each of thetouch regions may be compared with previous coordinates of the touchregions to determine positioning changes of the objects touching thetouch screen or whether or not touching objects have been added orsubtracted or whether a particular object is being tapped.

FIGS. 18 and 19 are side elevation views of an electronic device 350, inaccordance with multiple embodiments of the present invention. Theelectronic device 350 includes an LCD display 352 and a transparenttouch screen 354 positioned over the LCD display 352. The touch screen354 includes a protective sheet 356, one or more sensing layers 358, anda bottom glass member 360. In this embodiment, the bottom glass member360 is the front glass of the LCD display 352. Further, the sensinglayers 358 may be configured for either self or mutual capacitance asdescribed above. The sensing layers 358 generally include a plurality ofinterconnects at the edge of the touch screen for coupling the sensinglayer 358 to a sensing circuit (not shown). By way of example, thesensing layer 358 may be electrically coupled to the sensing circuitthrough one or more flex circuits 362, which are attached to the sidesof the touch screen 354.

As shown, the LCD display 352 and touch screen 354 are disposed within ahousing 364. The housing 364 serves to cover and support thesecomponents in their assembled position within the electronic device 350.The housing 364 provides a space for placing the LCD display 352 andtouch screen 354 as well as an opening 366 so that the display screencan be seen through the housing 364. In one embodiment, as shown in FIG.18, the housing 364 includes a facade 370 for covering the sides the LCDdisplay 352 and touch screen 354. Although not shown in great detail,the facade 370 is positioned around the entire perimeter of the LCDdisplay 352 and touch screen 354. The facade 370 serves to hide theinterconnects leaving only the active area of the LCD display 352 andtouch screen 354 in view.

In another embodiment, as shown in FIG. 19, the housing 364 does notinclude a facade 370, but rather a mask 372 that is printed on interiorportion of the top glass 374 of the touch screen 354 that extendsbetween the sides of the housing 364. This particular arrangement makesthe mask 372 look submerged in the top glass 356. The mask 372 servesthe same function as the facade 370, but is a more elegant solution. Inone implementation, the mask 372 is a formed from high temperature blackpolymer. In the illustrated embodiment of FIG. 19, the touch screen 354is based on mutual capacitance sensing and thus the sensing layer 358includes driving lines 376 and sensing lines 378. The driving lines 376are disposed on the top glass 356 and the mask 372, and the sensinglines 378 are disposed on the bottom glass 360. The driving lines andsensing lines 376 and 378 are insulated from one another via a spacer380. The spacer 380 may for example be a clear piece of plastic withoptical matching materials retained therein or applied thereto.

In one embodiment and referring to both FIGS. 18 and 19, the electronicdevice 350 corresponds to a tablet computer. In this embodiment, thehousing 364 also encloses various integrated circuit chips and othercircuitry 382 that provide computing operations for the tablet computer.By way of example, the integrated circuit chips and other circuitry mayinclude a microprocessor, motherboard, Read-Only Memory (ROM),Random-Access Memory (RAM), a hard drive, a disk drive, a battery, andvarious input/output support devices.

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. For example, although the touchscreen was primarily directed at capacitive sensing, it should be notedthat some or all of the features described herein may be applied toother sensing methodologies. It should also be noted that there are manyalternative ways of implementing the methods and apparatuses of thepresent invention. It is therefore intended that the following appendedclaims be interpreted as including all such alterations, permutations,and equivalents as fall within the true spirit and scope of the presentinvention.

What is claimed is:
 1. A digital signal processing method, comprising:receiving raw data, the raw data including values for each transparentcapacitive sensing node of a touch screen; filtering the raw data;generating gradient data; calculating the boundaries for touch regionsbase on the gradient data; and calculating the coordinates for eachtouch region.
 2. The method as recited in claim 1 wherein the boundariesare calculated using a watershed algorithm.
 3. The digital signalprocessing method as recited in claim 1, wherein, prior to receiving theraw data, converging analog signals from each transparent capacity esensing node of the touch screen into digitized signals corresponding tothe analog signals, the digital signals constituting the raw data. 4.The digital signal processing method as recited in claim 1, whereinfiltering the raw data comprises reducing noise in the raw data.
 5. Thedigital signal processing method as recited in claim 1, wherein the rawfor each transparent capacitive sensing node of a touch screencorresponds to a data point, and filtering the raw data removes singledata points that are not connected to other data points.
 6. The digitalsignal processing method as recited in claim 1, wherein filtering theraw data generates filtered raw data, and generating the gradient datais based on the filtered raw data.
 7. The digital signal processingmethod as recited in claim 1, wherein the transparent capacitive sensingnode of the touch screen produce a relatively low capacitive couplingvalue when a touch event occurs on the touch screen as compared to a notouch event, and wherein the gradient data corresponds to the capacitivecoupling values.
 8. The digital signal processing method as recited inclaim 1, wherein calculating the coordinates of each touch regioncomprises calculating a centroid of each touch region with the raw dataassociated with each touch region.
 9. The digital signal processingmethod as recited in claim 1, wherein, prior to receiving the raw data,converging analog signals from each transparent capacity e sensing nodeof the touch screen into digitized signals corresponding to the analogsignals, the digital signals constituting the raw data; wherein the rawfor each transparent capacitive sensing node of a touch screencorresponds to a data point, and filtering the raw data removes singledata points that are not connected to other data points; and whereinfiltering the raw data generates filtered raw data, and generating thegradient data is based on the filtered raw data.
 10. The digital signalprocessing method as recited in claim 9, wherein calculating thecoordinates of each touch region comprises calculating a centroid ofeach touch region with the raw data associated with each touch region.11. A computer system comprising: a processor configured to executeinstructions and to carry out operations associated with the computersystem; a display device that is operatively coupled to the processor; atouch screen that is operatively coupled to the processor, the touchscreen having transparent capacitive sensing nodes and providing analogdata indicative of a touch event on the touch screen; an analog todigital converter for receiving the analog data and providing digitalraw data at an output thereof; the processor operative in execution theinstructions for: receiving the digital raw data, the digital raw dataincluding values for each transparent capacitive sensing node of a touchscreen; filtering the digital raw data to provide filtered raw data;generating gradient data from the filtered raw data; calculating theboundaries for touch regions base on the gradient data; and calculatingthe coordinates for each touch region.
 12. The computer system asrecited in claim 11, wherein the processor calculates the boundariesusing a watershed algorithm.
 13. The computer system as recited in claim11, wherein the processor performs the filtering of the raw data forreducing noise in the raw data.
 14. The computer system as recited inclaim 11, wherein the raw for each transparent capacitive sensing nodeof a touch screen corresponds to a data point, and the processorperforms the filtering of the raw data for removing single data pointsthat are not connected to other data points.
 15. The computer system asrecited in claim 11, wherein the processor calculates the coordinates ofeach touch region by calculating a centroid of each touch region withthe digital raw data associated with each touch region.
 16. Anon-transitory computer readable medium including at least computer codeexecutable by a computer, the computer executing the computer code for:receiving raw data, the raw data including values for each transparentcapacitive sensing node of a touch screen; filtering the raw data;generating gradient data; calculating the boundaries for touch regionsbase on the gradient data; and calculating the coordinates for eachtouch region.
 17. The non-transitory computer readable medium as recitedin claim 16, wherein the boundaries are calculated using a watershedalgorithm.
 18. The non-transitory computer readable medium as recited inclaim 16, wherein filtering the raw data comprises reducing noise in theraw data.
 19. The non-transitory computer readable medium as recited inclaim 16, wherein the raw for each transparent capacitive sensing nodeof a touch screen corresponds to a data point, and filtering the rawdata removes single data points that are not connected to other datapoints.
 20. The non-transitory computer readable medium as recited inclaim 16, wherein filtering the raw data generates filtered raw data,and the computer executing the computer code generates the gradient datais based on the filtered raw data.
 21. The non-transitory computerreadable medium as recited in claim 16, wherein the computer executingthe computer code calculates the coordinates of each touch region bycalculating a centroid of each touch region with the raw data associatedwith each touch region.